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The characteristics of index-guided strip-buried heterostructure lasers are described. The lasers are grown by a two-step process, consisting of the initial 5-layer planar growth by MOCVD, and after etching to define the strip buried wave guide, recovery by Al 0.65 Ga 0.35 As using LPE. The devices are highly uniform, having 20 mA thresholds, quantum efficiencies of 0.65, and T 0 of 163°C. The TE polarized emission was in the lowest order transverse mode and consisted of ∼ 6 longitudinal modes. CW output powers of 50 mW per facet were obtained from lasers with reduced output reflectivity, and pulsed powers of 95 mW per facet from uncoated lasers have been obtained. The far-field angular widths were \sim 23\deg and \sim 50\deg in, and perpendicular to the junction plane, respectively. The total optical conversion efficiency of the coated laser emitting 50 mW CW was 41.5 percent.

A modified strip‐buried‐heterostructure (SBH) laser is described where the LPE growth process self‐aligns the current‐confining stripes with the active GaAs strips. With these lasers current thresholds have been reduced from ∼180 mA in previous SBH laser to ∼70 mA for active GaAs strips of 380×10×0.2 μm. Excellent linearity in light‐current characteristics and symmetry in laser output from both mirrors were obtained under both pulsed and cw operations. cw operation has been achieved at heat‐sink temperature as high as 115 °C. The current thresholds Ith have an exponential variation with temperature of the form Ith∝exp(T/T0) where T0 was 110 °K. Relaxation oscillation and self‐pulsation was not observed for lasers with clean transverse modes in pulsed response up to current injection levels as high as 4Ith.

Optical second harmonic generation from KH2PO4 and KD2 PO4 platelets was measured as a function of temperature, above and below the ferroelectric transition point, between 77 K and 300 K. The nonlinear process is expressed by a third rank susceptibility tensor relating the second harmonic polarization to a quadratic function of the applied fields. A phenomenological theory is developed to account for the observed changes in the linear and nonlinear susceptibilities at the transition point. Relations between the tensor elements above and below the ferroelectric transition are obtained. The difficulties encountered in the experiment in the ferroelectric phase due to domains, and in the interpretation of the experimental data are discussed. The effects of atomic substitution on the relative values of the second harmonic susceptibilities was investigated by measurements at 300 K on the following isomorphs: KH2PO4, KH2AsO4, KD2PO4 and NH4H2PO4. These substitutions have important effects on the low frequency dielectric and linear optical properties. (Author)

The temperature and concentration dependences of the visible emission of ${\mathrm{Er}}^{3+}$ in Y${\mathrm{F}}_{3}$ under infrared excitation of the $^{4}I_{\frac{11}{2}}$ levels have been measured. The infrared radiation is absorbed by ions initially in the ground state and two excitations subsequently combine, yielding an ion in a higher-energy state. The temperature dependence of the $^{4}S_{\frac{3}{2}}\ensuremath{\rightarrow}^{4}I_{\frac{15}{2}}$ emission has a broad maximum at 90\ifmmode^\circ\else\textdegree\fi{}K. The reduction in the emission for $Tl90$\ifmmode^\circ\else\textdegree\fi{}K results from the depopulation of the higher-energy crystal-field-split levels of the $^{4}I_{\frac{11}{2}}$ manifold which have a resonant match with the $^{4}F_{\frac{7}{2}}$ levels. For $Tg90$\ifmmode^\circ\else\textdegree\fi{}K the emission is increasingly quenched by ion-pair relaxation from $^{4}S_{\frac{3}{2}}$ via $^{2}H_{\frac{11}{2}}$. For the concentration range $0.01lxl0.1$, the $^{4}S_{\frac{3}{2}}$ emission is proportional to ${x}^{2.9}$ at 77\ifmmode^\circ\else\textdegree\fi{}K and to ${x}^{1.3}$ at 295\ifmmode^\circ\else\textdegree\fi{}K.

The inverse Faraday effect (IFE) occurs when circularly polarized light incident on a nonabsorbing crystal induces a magnetic moment proportional to the Verdet constant of that material, the proportionality constant being independent of the material. Some experimental details relating to the observation and proof of the IFE are presented. A microscopic, or quantum-mechanical, explanation of the IFE which also demonstrates its connection with the Faraday effect is given in terms of an optically induced "effective Hamiltonian" ${\mathcal{H}}_{\mathrm{eff}}$. Conventional calculations of the optical constants like the Verdet constant compute optical-frequency polarizabilities for a given electronic configuration. It is shown here that these same constants are obtained by computing the average effects that optical fields have on the atomic configuration. The optically induced ${\mathcal{H}}_{\mathrm{eff}}$ is linearly dependent on the low-frequency components of $E(t)E(t)$ and one can show the thermal average ${〈{\mathcal{H}}_{\mathrm{eff}}〉}_{\mathrm{thermal}}$ is equal to the temporl average ${〈\mathbf{E}(t)\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{\ensuremath{\varepsilon}}\ifmmode\cdot\else\textperiodcentered\fi{}(\mathbf{E}t)〉}_{\mathrm{time}}$. Both the Verdet constant and the IFE coefficient arise from a thermal average of the same term in ${\mathcal{H}}_{\mathrm{eff}}$. Similarly the Cotton-Mouton effect and its inverse arise from one other term in ${\mathcal{H}}_{\mathrm{eff}}$. Definition of ${\mathcal{H}}_{\mathrm{eff}}$ is one technique for linearizing some nonlinear optical problems. Following linearization one obtains Kramers-Kronig-type dispersion relations between constants of seemingly different phenomena. For example, a Kramers-Kronig relation is obtained between the Verdet constant and the gain coefficient for stimulated Raman scattering by paramagnetic ions in a large dc magnetic field. The effective Hamiltonian is explicitly evaluated from some illustrative examples and its general phenomenological form for a paramagnetic ion in cubic symmetry is written down and discussed.

The relative emission per ion and the lifetime have been obtained as a function of Tb concentration for the $^{5}D_{4}$ to $^{7}F_{J}$ transitions in ${({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x})}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ crystals. At 297 \ifmmode^\circ\else\textdegree\fi{}K both are concentration independent for $xl0.3$ and decrease as ${x}^{4.6\ifmmode\pm\else\textpm\fi{}0.2}$ for $xg0.4$ up to about a factor ${10}^{2}$ for ${\mathrm{Tb}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$. From the time dependence of the intrinsic ${\mathrm{Tb}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$ luminescence the initial nonexponential portion of the decay is shown to be consistent with direct dipolar transfer to nonradiative sinks. The later part of the decay is exponential and involves resonant ${\mathrm{Tb}}^{3+}$-${\mathrm{Tb}}^{3+}$ migration to the sinks. The direct transfer is found to be relatively temperature insensitive, but migration is not. There is little migration at low temperatures but for $Tg8\ifmmode^\circ\else\textdegree\fi{}$K, where the higher-energy $^{5}D_{4}$ levels begin to be populated, the migration rate increases rapidly. The temperature dependence of the migration constant $D$ was calculated using the level populations and oscillator strengths. The migration contribution to the exponential decay is proportional to ${D}^{\frac{3}{4}}$ indicating the ${\mathrm{Tb}}^{3+}$-${\mathrm{Tb}}^{3+}$ transfer also involves dipolar interactions. Impurity-perturbed ${\mathrm{Tb}}^{3+}$ emission is observed for $Tl12\ifmmode^\circ\else\textdegree\fi{}$K. These ions are mainly populated by direct dipole transfer from the intrinsic ions. Multiple-ion-decay processes involving the deexcitation of an ion in the $^{5}D_{4}$ state and the simultaneous excitation of three or more neighboring ${\mathrm{Tb}}^{3+}$ ions are shown to be negligible at low temperatures.

The polarized optical-absorption spectrum of the hexagonal ferrimagnet RbNi${\mathrm{F}}_{3}$ is considered for the transitions from the ground state $^{3}A_{2}$ to excited states $^{3}T_{2}$ and $^{1}{T}_{2}^{a}$. For the $^{3}T_{2}$ manifold, an effective Hamiltonian is constructed and its parameters are adjusted to match the levels of the observed spectrum. Estimates are made for the excited-state exchange field; however, because the exchange interaction appears somewhat anisotropic, the preciseness of these estimates is limited by the adequacy of the anisotropic exchange Hamiltonian to describe the effects produced by reorientation of the exchange field direction. Oscillator strengths, calculated from the resulting wave functions are in reasonable agreement with the measured values for this manifold. The reorientation of the exchange field from the basal plane to the $c$-axis direction is seen to manifest itself in a very direct way through the behavior of the oscillator strengths of some of the features in the $^{1}{T}_{2}^{a}$ manifold.

The rate equations for green fluorescence of the Yb3+–Er3+ doubly doped quantum counter are solved for the case of an infrared pump at the Yb3+ 2F7/2−2F5/2 transition. The successive transfer of excitation from two Yb3+ ions to the Er3+ produces green emission from the Er3+ 4S3/2 level. The increase of the 4S3/2 lifetime with increasing Yb3+ concentration in Na0.5(Y, Yb, Er)0.5WO4 confirms the consecutive transfer model of Auzel. Emission from Er3+ in a solid solution of divalent cation tungstates or molybdates (having the scheelite structure) under long‐wave ultraviolet excitation is proportional to the inverse of the cation‐anion separation, and hence the binding energy. The emission under infrared excitation is relatively independent of this separation.

Recent observations of RE 3+ terminated Cr 3+ fluorescence in Cr 3+ doped rare earth garnets are reviewed. At 4.2°K we observe (a) RE 3+ fluorescence, (b) Cr 3+ emission from the 2 E to 4 A 2 levels and (c) emission originating on the lowest 2 E level and terminating on the RE 3+ levels. The coupling results from exchange which gives a spin dependent dipole moment P = Σπ ij s i (Cr) . s j (RE). The matrix element of P between 2 E and 4 A 2 does not vanish because of the anisotropy of the Cr 3+ orbitals. For Eu 3 Ga 5 O 12 weak pair lines are found for J > 2; the pair emission to J = 1, 2 is obscured by a strong vibronic sideband. In Yb 3 Al 5 O 12 the Cr 3+ lines are broadened by exchange and pair transitions terminating on the levels of the 2 F 7/2 and 2 F 5/2 states are observed. The separation of the pair lines from the 2 E → 4 A 2 emission is generally in good agreement with the RE energy levels.

The optical spectrum and exchange splittings of the two types of nearest neighbor Cr3+ pairs in orthorhombic YAlO3 have been studied. The emission spectrum from 7200 to 7350 A yields the ground state exchange −JS.S+j(S.S)2 with Ja=−24.7, ja=−0.66 cm−1 and Jb=−26.2 and jb=−0.91 cm−1. From the shift of the lines under uniaxial compression along the crystal z axis we conclude these values correspond, respectively, to pairs whose axes are in the xy plane and along the z axis. The energies of several pair levels with one ion in 2E and the other in 4A2, having S=1 and 2 have been obtained. Selective enhancement of nn pair luminescence is observed when the excitation energy is at about twice the single ion 2E energy. The excitation and absorption spectra indicate these are pair levels corresponding to both ions in the 2E state and have S=0 and 1. The single ion transitions are magnetic dipole in agreement with Cr3+ being at a center of inversion. The pair lines are electric dipole, and the strongest transitions ...

The magnetization of ruby in a magnetic field at 300\ifmmode^\circ\else\textdegree\fi{}K is changed when the ruby is optically pumped with linearly polarized radiation from a $Q$-switched ruby laser. With a magnetic field parallel to the trigonal axis, laser light polarized parallel to this axis induces transitions from the spin \ifmmode\pm\else\textpm\fi{}\textonehalf{} levels of the $^{4}A_{2}$ ground state to the levels of the $\overline{E}(^{2}E)$ excited state. The change in ${M}_{z}$ is linearly proportional to $H$ except near the anticrossing points of the $^{4}A_{2}$ spin levels at 2.07 and 4.14 kG. At these field strengths, there is an enhancement of the magnetization caused by state mixing of the $^{4}A_{2}$ wave functions. When $H$ has a small component perpendicular to the $z$ axis, a magnetization is detected parallel to this component in the vicinity of 4.14 kG. The effect requires a long ground-state relaxation time. In a separate experiment, the relaxation of ${M}_{z}$ was found to vary from 0.13 \ensuremath{\mu}sec in zero magnetic field to a constant value of 0.57 \ensuremath{\mu}sec for fields above 60 G.

Single longitudinal mode operation of cleaved‐coupled‐cavity lasers formed by recleaving of 1.5‐μm InGaAsP buried crescent lasers is investigated as a function of bias current, temperature, and modulation frequency. The two‐cavity lasers are made to operate in a stable single mode by adjusting the bias levels of the electrically isolated and optically coupled sections. The wavelength stability with temperature results in a change of only 0.48 A/°C over a range of 14 °C. Single mode operation is preserved under direct modulation at rates as high as 1 Gb/s. The reduction in linewidth and the absence of partition noise makes these lasers useful for optical transmission through highly dispersive single mode fibers.

Double heterostructures consisting of InAs0.91 Sb0.09 active layers with Al0.5 Ga0.5Sb cladding layers were grown by molecular beam epitaxy on GaSb substrates. Optically pumped laser emission at 3.9 μm was observed from 80 to 135 K with an exponentially dependent threshold with T0=17 K. At 80 K the threshold corresponds to an effective current of 4 kA/cm2. This value represents a significant reduction when compared with previous results. For a 1‐μm‐thick active layer the full angular width of the far field at the half intensity point normal to the junction is 40° and is in reasonable agreement with the width calculated from the guide and cladding refractive indices.

An integrated multilayer laser consisting of three double heterostructure GaAs laser diodes connected in series by reversed biased p+n+ tunnel junctions have been grown by molecular beam epitaxy. The lasers operate at currents comparable to single double heterostructure lasers but at approximately three times the single laser voltage.

Proton bombardment at 3×1015–1016‐cm−2 dosage level and 300 keV has been used to introduce a ∼4‐μm‐long nonradiative region at one of the mirror facets. The region acts as a saturable absorber and converts the initially temporally stable optical emission to a pulsating behavior with a repetition rate in the 0.5–3‐GHz range.

Waveguiding of 1.0642‐μm radiation and nonphase‐matched second harmonic generation have been observed in a 200‐A‐thick GaP waveguide grown by molecular beam epitaxy on a (111) ‐oriented CaF2 substrate.

We have fabricated low‐threshold, high‐quantum‐efficiency, room‐temperature AlGaAs‐GaAs double‐heterojunction injection lasers from epitaxial structures grown by metalorganic chemical vapor deposition directly on Si substrates. These devices have broad‐area (125 μm×250 μm) pulsed threshold current densities as low as Jth =3.5 kA/cm2 at ∼23 °C. Ridge‐waveguide stripe‐geometry lasers (5 μm×250 μm) have pulsed threshold currents as low as 130 mA at ∼23 °C. These stripe‐geometry lasers have total external differential quantum efficiencies as high as ηext ∼70%, a value equal to the ηext measured for similar double‐heterostructure lasers grown on GaAs substrates. These are the lowest threshold currents and highest external quantum efficiencies yet reported for lasers grown on Si substrates.

Arrays of five InGaAsP buried‐cresent large‐optical‐cavity lasers operating at 1.3 μm are described. The monolithically integrated arrays have threshold as low as 60 mA, external quantum efficiencies η≊55%, and operate in the fundamental transverse mode up to 50 mW per facet at room temperature. Despite the very close center to center spacing of 8 μm, no electrical or optical interaction between lasers has been observed.

A diffraction‐coupled laser array has been actively mode locked in an external cavity to yield Gaussian pulses as short a 61‐ps full width at half‐maximum with a peak power of 1.1 W and an average power of 0.07 W. The array consists of 10 lasers, each 3 μm wide with 9‐μm center to center spacing. It emits with a stable double‐lobed far‐field pattern characteristic of the out‐of‐phase coupling between neighboring lasers. These arrays may be useful where high peak as well as high average optical powers are required.

We report optically pumped laser oscillation from multilayer heterostructures consisting of alternating layers of GaAs and Al0.2Ga0.8As. Very thin GaAs layers (50−500 A) exhibit one−dimensional bound states above the band gap of bulk GaAs. The laser oscillation occurs at energies which are slightly below the exciton associated with the lowest energy n=1 bound state.

Simple, self‐aligned phase‐coupled laser arrays consisting of ten 3‐μm‐wide stripes are described. The current flow was confined to the stripes by a Schottky barrier over the remainder of the laser chip. This process, applied to the AlGaAs graded‐index structures grown by metalorganic vapor phase epitaxy, produced arrays with threshold currents as low as 20 mA/stripe. The devices are capable of output powers of up to 1 W/facet and operate at temperatures as high as 100 °C with a stable far‐field pattern. In addition, novel information on the phase coupling in these gain‐guided arrays has been obtained.

Using a tunable laser operating near 2 μm we have observed second harmonic generation in a GaAs‐Al0.3Ga0.7As multilayer. Phase matching of the backward‐traveling harmonic wave is observed and corresponds to k2=2(k1−κ)

An array of 16 individual addressable lasers with 50‐μm center spacing has been monolithically integrated on a GaAs chip and cw bonded to a Si submount and copper heat sink. The lasers have the loss stabilized buried heterostructure geometry with separate optical and carrier confinement. The advantages of this laser geometry for integration into arrays are described.

It is found experimentally that the linewidth of a grating loaded external cavity semiconductor laser is inversely proportional to the square of the linear dimension of the overall cavity. This observed behavior is consistent with the existing theories on the linewidth of a laser with an extended passive cavity. A slope of 6.5×105 Hz cm2 is obtained from least‐squares fitting the linewidth vs 1/(cavity length)2 curve at 1 mW of power. However, the linewidth reaches a lower limit when the cavity length is extended beyond a certain limit. This result suggests that additional phase noise term should be included in the calculation of linewidths of these extended cavity semiconductor lasers. We also report a value as small as 18 kHz mW in the linewidth vs 1/(power) curve.

The warpage of GaAs‐on‐Si wafers, caused by the different thermal expansion coefficients of GaAs and Si, has been studied as a function of the GaAs thickness on 3‐in.‐diam Si wafers. The warpage increases from 7 to 52 μm as the GaAs layer thickness increases from 1.2 to 4.2 μm. Under vacuum clamping conditions the GaAs/Si wafers can be forced to the original flatness. By growing GaAs selectively through a Si shadow mask as islands of 1 mm×1 mm size with a periodicity of 2 mm in a 5 cm×5 cm central area of the wafer, the warpage is reduced considerably. Spatially resolved cathodoluminescence (CL) spectra indicated that the tensile strain is reduced significantly within 10 μm from the edge of the growth. Near the edge, the CL intensity is also increased indicating a reduction in nonradiative recombination at defects. The use of the Si shadow mask to obtain patterned growth is relatively simple, requiring no processing step before or after the growth, and has a great potential in the integration of GaAs and ...

We report the observation of bursts of transform‐limited 0.65‐psec pulses at 1‐GHz repetition rates by passive mode locking of a buried optical guide laser in an external cavity. The lasers contain a saturable absorber at the exit facet, specifically introduced by 600‐keV proton bombardment at a 3×1015‐ cm−2 dosage level.

Tunable stimualted emission of radiation is achieved in AlxGa1−xAs/GaAs double heterostructures, in which the waveguiding GaAs region consists of a delta‐doped doping superlattice. The low‐temperature emission energy is 45 meV below the bulk band gap of GaAs for homogeneous optical excitation of the Fabry–Perot cavity. The emission energy is continuously tunable over 35 A by inhomogeneous excitation of the cavity.

The growth by molecular‐beam epitaxy of high‐quality Ga0.85In0.15As0.13Sb0.87 active layers with Al0.4Ga0.6As0.035Sb0.965 cladding layers on GaSb substrates by molecular‐beam epitaxy is reported. The lattice match of the active layer to the substrate is Δa/a ∼4 ×10−3. Optically pumped laser oscillation was observed from 80 to 300 K with T0=55 K for T

The growth conditions to achieve high‐quality InAsSb alloy and abrupt InAsSb/GaSb heterostructure by molecular‐beam epitaxy are described. The present results indicate that optical pyrometry is a reliable method to determine the growth temperature, and a stable substrate temperature is of critical importance in achieving homogeneous InAsSb composition throughout the growth period. The quality of these epilayers is evaluated by double x‐ray diffraction measurement, reflection high‐energy electron diffraction study, Nomarsky microscopy, and low‐temperature photoluminescence. The optical quality is further demonstrated by the optically pumped coherent emission at ∼3.9 μm observed from an InAsSb active layer.

Separate confinement heterostructure wafers grown by gas source molecular beam epitaxy have been used to prepare ridge waveguide lasers operating up to 50 °C. Laser threshold currents varied from 45 to 65 mA at room temperature and output powers up to 9 mW have been obtained with the external quantum efficiency of ∼36%. Gain profile measurements indicate excellent material uniformity. Frequency response flat to at least 2 GHz is consistent with the material free of interfacial traps or any capacitive shunt paths.

It is shown that the deep level (∼1.0 eV) luminescence observed in double‐heterostructure lasers originates from the E3 radiation damage trap (Ga vacancy) or a closely related vacancy‐donor complex in the n‐type GaAs substrate region rather than in the active region as had been reported previously.

The optical pulsations in the output of semiconductor lasers are accompanied by a time variation of the diode voltage. During the optical pulse the voltage decreases by ≈2.5 mV, corresponding to a decrease in carrier population. In the interval between pulses the voltage recovers exponentialy with a 1.3±0.2‐nsec time constant to its prepulse value as a result of carrier injection into the active region.

We attribute the single longitudinal mode operation of some Er‐doped 1.5‐μm InGaAsP lasers, observed here, to inhomogeneities in the active layer resulting from the Er. These results do not rule out the possibility of gain narrowing by the Er when Er is properly incorporated in the active layer.

The measured birefringence of ultrathin AlxGa1−xAs‐GaAs multilayers grown by molecular beam epitaxy is shown to result from the difference in the effective refractive indices for transverse electric and magnetic polarizations and from the quantum‐size effect of the one‐dimensionally confined carriers in the GaAs potential wells.

Low threshold, optically pumped laser oscillation has been obtained using AlGaAs/GaAs double heterostructures grown on Ge‐coated Si substrates. The optical pump power for threshold is comparable to similar heterostructures grown on GaAs substrates. Between 20 and 85 °C the threshold temperature dependence is exponential with T0=160 °C. The laser wavelength and the peak of the spontaneous emission of lasers grown on Si substrates are shifted to longer wavelengths relative to bulk GaAs. This results largely from the strain in the plane of the epilayer produced by the difference in the thermal contraction of the layers and the Si substrate on cooling from the growth temperature.

Using a tunable parametric oscillator operating near 2 μm, we have observed second‐harmonic generation in a GaAs double‐heterostructure waveguide in the region of phase matching. The harmonic intensity is strongly peaked when the guide propagation constants of the TE (m=0) fundamental and TM (m=2) harmonic are equal. Away from phase matching, the characteristic effects of strong focusing in the plane of the guide are observed. These are the one‐dimensional analogs of the harmonic generation effects observed using two‐dimensional focused laser beams.

A monolithic array of five noninteracting buried crescent lasers has been optically multiplexed using an external cavity with a grating as a dispersive element. The lasers have a center to center separation of 8 μm, and with an external cavity consisting of a 4‐mm focal length lens and a 600‐line/mm grating used in second order, the lasers emit at ≊1.31 μm in essentially single longitudinal modes separated by 19.6 A. Single longitudinal mode operation has also been obtained using a cleaved coupled cavity (C3) laser array. In this case the dominant mode is determined by the coherent interference of the mode spectrum of the two subcavities.

The measured birefringence of the refractive indices of GaAs‐AlAs multilayers grown by molecular beam epitaxy is found to vary from 0.056 at 0.9 μm to 0.042 at 1.1 μm.

Using graded refractive index, single quantum well GaAs lasers grown by metalorganic chemical vapor deposition on Si substrates, we have obtained injection lasers with broad area pulsed thresholds of 3.5 kA/cm2 at 300 K. With the current flow restricted to 5‐μm‐wide stripes, pulsed thresholds of 130 mA and differential quantum efficiencies of 70% were obtained at 300 K. Pulsed oscillation has been obtained up to 375 K and continuous oscillation up to 160 K. The rapid degradation of the lasers suggests the growth of nonradiative regions in the active layer.

We report a new lateral selective‐area growth by liquid‐phase epitaxy with the preparation of a new buried‐heterostructure laser, the lateral double‐barrier buried‐heterostructure (DBBH) laser, as an illustrative example. The DBBH laser so prepared operated in a stable clean fundamental mode with reduced optical scattering losses due to sidewall roughness of the etched mesa. Pulsed operation was achieved at temperatures as high as 280 °C. This new selective‐area growth can also be used to form guided wave integrated microlens systems.

Double heterostructures consisting of GaSb active layers with Al0.4Ga0.6Sb cladding layers were grown by molecular beam heteroepitaxy on Si substrates. The intrinsic ∼12% lattice mismatch between the GaSb and the Si at the growth temperature is largely taken up by a GaSb/AlSb superlattice. The larger thermal contraction of the GaSb layer relative to that of Si causes the GaSb layer to be under severe dilatory strain relative to the Si substrate at room temperature. Optically pumped laser emission ranging from 1.62 μm at 80 K to 1.82 μm at 350 K was observed. The threshold varied somewhat nonexponentially with temperature, with a change in slope at ∼250 K. The exponential threshold‐temperature dependences at 80 and 300 K are T0=158 and 100 K, respectively, and are higher than previously reported for GaSb lasers. At 300 K the threshold corresponds to an effective current of 12 kA/cm2.

Second harmonic generation was measured from a thin AlAs‐GaAs single‐crystal multilayer using a laser tunable from 1.9 to 2.2 μm as fundamental. Due to propagation effects in the multilayers, the index mismatch nTM(2ω)−nTE(ω), obtained from the coherence length oscillations, is smaller than for the corresponding alloy.